The present invention relates to subterranean well cementing operations, and more particularly, to methods of using cement compositions comprising phosphate compounds in subterranean formations.
Hydraulic cement compositions commonly are utilized in subterranean operations, particularly subterranean well completion and remedial operations. For example, hydraulic cement compositions are used in primary cementing operations whereby pipe strings, such as casing and liners, are cemented in well bores. In performing primary cementing, a hydraulic cement composition is pumped into an annular space between the walls of a well bore and the exterior surface of the pipe string disposed therein. The cement composition sets in the annular space, thereby forming therein an annular sheath of hardened, substantially impermeable cement that supports and positions the pipe string in the well bore and bonds the exterior surface of the pipe string to the walls of the well bore. Hydraulic cement compositions also are used in remedial cementing operations, such as plugging highly permeable zones or fractures in well bores, plugging cracks and holes in pipe strings, and the like.
Conventional well completion operations commonly involve a period of time wherein subsequent operations (e.g., casing perforation operations, stimulation operations, and the like) may be delayed in order to permit the cement composition to set, and develop sufficient compressive strength in the subterranean formation to permit further drilling to be performed. These time periods may be referred to as “waiting-on-cement time” or “WOC time.” Given the high cost to place a drilling rig or workover rig on a job site, excessive WOC time may increase the cost of performing subterranean operations dramatically on a particular well.
Conventional attempts to reduce WOC time commonly have involved the use of magnesium phosphate cement compositions, which are known to set relatively rapidly. However, in some cases conventional magnesium phosphate cement compositions may set so rapidly that a retarder must be included to permit pumping of the magnesium phosphate cement composition to its desired location in a subterranean formation. Though the inclusion of a retarder in the magnesium phosphate cement composition may be suitable in certain circumstances, such retarders often fail to retard the setting of the magnesium phosphate cement compositions at temperatures of about 200° F. and above.